The invention relates to electrostatic collectors or precipitators, including for diesel engine electrostatic crankcase ventilation systems for blowby gas for removing suspended particulate matter including oil droplets from the blowby gas.
Electrostatic collectors or precipitators, including for diesel engine electrostatic crankcase ventilation systems, are known in the prior art. In its simplest form, a high voltage corona discharge electrode is placed in the center of a grounded tube or canister forming an annular ground plane providing a collector electrode around the discharge electrode. A high DC voltage, such as several thousands volts, e.g. 15 kV, on the center discharge electrode causes a corona discharge to develop near the electrode due to high electric field intensity. This creates charge carriers that cause the ionization of the gas in the gap between the high voltage electrode and the ground electrode. As the gas containing suspended particles flows through this region, the particles are electrically charged by the ions. The charged particles are then precipitated electrostatically by the electric field onto the interior surface of the collecting tube or canister.
Electrostatic collectors have been used in diesel engine crankcase ventilation systems for removing suspended particulate matter including oil droplets from the blowby gas, for example so that the blowby gas can be returned to the atmosphere, or to the fresh air intake side of the diesel engine for further combustion thus providing a blowby gas recirculation system.
The corona discharge electrode assembly commonly used in the prior art has a holder or bobbin with a 0.006 inch diameter wire strung in a diagonal direction. The bobbin is provided by a central drum extending along an axis and having a pair of flanges axially spaced along the drum and extending radially outwardly therefrom. The wire is a continuous member strung from back and forth between the annular flanges to provide a plurality of segments supported by and extending between the annular flanges and strung axially and partially spirally diagonally between the flanges. The inside of the drum is hollow.
The present invention provides a compact, multistage, space-efficient electrostatic collector. The present construction improves utilization of space within a package allowing for a reduction in package size or an increase in flow rating for the same package size. Effective residence time is increased by incorporating corona generation and particle collection in an inner annular passage by using the formerly unused hollow inside of the drum.
Customer requirements continue favoring smaller packaging in underhood components in internal combustion engine applications. These customer demands can be better met if all available space is used to maximum extent. The present invention not only provides better utilization of available space but also provides improved performance including within a small space-efficient package size. The improved performance is provided by increasing charged particle residence time. In one aspect, collecting zones are provided both inside and outside of the electrode drum, increasing residence time without lengthening the electrode, thus providing longer residence time, higher corona discharge efficiency, and better space efficiency. The use of both inner and outer charging and collection stages effectively increases residence time by increasing the effective length of the electrode and corona discharge zone.